For achieving the higher efficiency and power density, the H-bridge power factor correction (PFC) circuit possesses a trend of replacing the conventional boost PFC circuit nowadays.
As an example, for an H-bridge PFC circuit in FIG. 1, its on-state loss is smaller than that of a conventional boost PFC circuit, i.e. a conventional rectifier bridge pluses a boost circuit structure. Since the rectifier bridge is omitted in the H-bridge PFC, the efficiency of the circuit is increased dramatically.
FIG. 1 shows a circuit diagram of an H-bridge PFC circuit in the prior art, which possesses a higher efficiency while comparing with the conventional boost PFC circuit. In FIG. 1, Vin is an AC power source; Vout is an output voltage; L is an inductor; C1 is an output capacitor; D1, D2, D3 and D4 are rectifier diodes, which form two bridge arms of an H-bridge. T1 and T2 are two switch elements of the H-bridge, and the series-connected T1 and T2 form a bidirectional switch. As an example, the bidirectional switch comprises the two inverse series-connected MOSFETs as shown in FIG. 1. The bidirectional switch connects to the middle points A and B of the two bridge arms with the anodes of their body diodes connected together. And the middle point A connects to Vin through the inductor L, while B connects to Vin directly. T1 and T2 are turned on and off simultaneously. The AC input voltage charges the inductor L when T1 and T2 are turned on and at the same time the four rectifier diodes D1, D2, D3 and D4 are off. If T1 and T2 are turned off and the voltage value at A is larger than that at B, D1 and D3 are turned on, D2 and D4 are turned off and the inductor L outputs energy to the output capacitor C1. If T1 and T2 are turned off and the voltage value at B is larger than that at A, D2 and D4 are turned on, D1 and D3 are turned off and the inductor L also outputs energy to the output capacitor C1.
In the circuit of FIG. 1, the two switches T1 and T2 are driven under floating ground structure, and a conventional bootstrap driver circuit, such as circuits in the blocks 1 and 2 of FIG. 3(a), can be employed. As shown in the block 1 of FIG. 3(a), a conventional bootstrap circuit includes capacitors C2, C3 and a bootstrap switch element such as diode D5. Capacitor C3 is a bootstrap capacitor, and a bootstrap voltage across this capacitor provides energy to drive the two switches. And the energy in the capacitor C2 is charged to C3 through the bootstrap diode D5. As shown in the block 2 of FIG. 3(a), a conventional driving circuit provides gate driving pulses to the two switches T1 and T2, which could be any of the driving circuit structures known by the person with the ordinary skill in the art. In the H-bridge circuit as shown in FIG. 3(a), terminal S connects to terminal G either through the body diode of T2 and diode D3 (when the value at A is larger than that at B), or through the body diode of T1 and diode D4 (when the voltage value at B is larger than that at A) when the two switches T1 and T2 are turned off. At this moment, S and G have almost the same voltage potential, diode D5 is on, and the energy stored in the storage capacitor C2 charges the bootstrap capacitor C3 through diode D5. When T1 and T2 are turned on, S floats (not connected to G) and the energy stored in capacitor C3 from the above-mentioned process is to provide energy to the driving circuit in the block 2 of FIG. 3(a).
FIG. 2 shows a circuit diagram of another H-bridge PFC circuit in the prior art. Output capacitors C1 and C4 are connected in series and forms a bridge arm; and rectifier diodes D1 and D4 form another bridge arm. T1 and T2 are two series-connected switch elements to form a bidirectional switch which connects the middle points of the two bridge arms A and B. And A connects to Vin through the inductor L, and B connects to Vin directly. T1 and T2 are turned on and off simultaneously. The AC input voltage charges the inductor L and the rectifier diodes D1 and D4 are turned off when T1 and T2 are turned on. If the voltage value at A is larger than that at B, D1 is on, D4 is off and the inductor L outputs energy to the output capacitor C1 when T1 and T2 are turned off. If the voltage value at B is larger than that at A, D4 is on, D1 is off and the inductor L also outputs energy to the output capacitor C4 when T1 and T2 are turned off.
In the circuit of FIG. 2, the two switches T1 and T2 are driven under floating ground structure too, and a conventional bootstrap driver circuit, such as circuits in the blocks 1 and 2 of FIG. 3(b), can also be employed.
The bootstrapped driver circuit can only operate normally under the condition that a bootstrap path is provided. The bootstrap path of the H-bridge circuit in FIG. 3(a) would be lost under certain circumstances. For example, under the unloaded condition, light loaded condition, or around the zero-crossings of AC input voltage, the diodes D3 or D4 on the bridge arms is off due to lack of sufficient current. Thus, S and G could not form almost the same voltage potential, and then the bootstrap path could not be formed. Then, C3 could not obtain the energy from C2 through D5, and could not provide energy to the driving circuit in the block 2 of FIG. 3(a). Besides, there are circumstances that the bootstrap path might be lost e.g. during the starting stage of the H-bridge PFC circuit in FIG. 3(a). Since at the beginning of the starting stage, T1 and T2 are not operated, and the AC input voltage engages the uncontrollable rectification through diodes D1, D2, D3 and D4 to charge C1. And then the uncontrollable rectification is stopped and diodes D1, D2, D3 and D4 are off when C1 is charged to the peak value of the AC input voltage. If the voltage across the bootstrap capacitor C3 is not built up at the moment which means the voltage across C3 is not enough to provide energy to the driving circuit to drive switch T1, T2, the bootstrap path is not existed since diodes D1, D2, D3 and D4 are off even if the voltage across capacitor C2 is built up.
Similar problems could also appear in the H-bridge circuit of FIG. 3(b).
The above-mentioned H-bridge circuits are mainly applied to the PFC circuits. Actually, the applications of the H-bridge circuits are not limited to this, and the H-bridge circuits could be applied to all the circuits with AC input and DC output. But no matter what occasion, there are possibilities that the above-mentioned problems exist as far as the conventional bootstrapped driving mode is employed.
Keeping the drawbacks of the prior arts in mind, and employing experiments and research full-heartily and persistently, the applicant finally conceived an H-bridge circuit having an energy compensation circuit and a controlling method thereof.